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How do you simplify ##cos 2x = (1-tan^2x)/(1+tan^2x)##?
##Cos2x## = ##Cos2x##
##Cos2x## = ##(1 - tan^2x)/(1+tan^2x)##
##Cos2x## = ##(1 - tan^2x)/(Sec^2x)##
##Cos2x## = ##(1 - tan^2x)/(1/Cos^2x)##
##Cos2x## = ##(1 - sin^2x/Cos^2x)*(Cos^2x)##
##Cos2x## = ##Cos^2x - sin^2x##
##Cos2x## = ##Cos2x##
hope it helps